NLC – Noctilucent cloud
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NLC is popping up, latterly in MikeL’s thread ‘Clouds in black and white’ q.v. for Bill’s post at about the same date/time as this thread begins; MikeL’s is tagged NLC. So I would like to add the link below to this forum – we may have seen it on the old forum, perhaps posted by Noctilucy:
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Hi,
The past few postings got me thinking….A decade ago I put together a rather basic page on NLC’s after we had had a couple of years of tremendous displays. The NLCNET and forum were coming into reality at this time and there was a lot of interest.
It’s a bit basic, HTML 1.whatever in those days, no fancy graphics!
I’ve added a few more recent videos now but it might give people who are unfamiliar with the phenomena some background. It was a deliberate attempt to moderate some of the more extreme claims made about the “increasing” NLC activity.
Cheers,
Bill. -
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Bill, your data will be an excellent reference for this Forum. I note you say NLC are quite common in the N Hemisphere (I have not seen them). I just posted in the Above The Clouds topic a random set of pictures from the CAS Gallery, all by Captain Ghorbal – of the ten pictures, two are NLC. (He was active 2008 – 2010).
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Hi Marsha,
Whilst you’re on the lower edge of the envelope I’ve seen reports from the US so there’s a chance.
I didn’t make the point about the solar cycle very clearly. What I mean is that NLC do get more frequent when the solar cycle is at its low point, then they reduce a bit when the solar cycle peaks but there is a delay in this effect. Roughly speaking if the solar max was last year the NLC occurence would probably be at a minimum this year. I hope that makes a bit more sense.
Anyway, keep a lookout low to the northern horizon through the summer nights June to July. I hope they oblige for you.
Cheers,
Bill.
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Hi Hygge,
Thanks, Whilst they’ve not been quite so prominent over the past couple years I would still use the word “common”. The very best displays last summer in the northern hemisphere (that I recorded) happened in the wee hours, 1am-3am local. That quite reasonably deters some people as there is never any guarantee!The occurence of NLC also show a clear anti phase relationship to solar activity (with some time lag). So, even with a weak solar max, the numbers are down a little at the moment. If you look through the archives on NLCNET you’ll see that NLC are recorded on most nights from somewhere across Europe through June and July, so they are there. It’s just they are often missed at any given location due to tropo cloud cover.
Here in the UK, particularly the NW mainland, even in summer the weather can put paid to seeing any.
What tends to catch peoples’ attention is when there is a really big “evening sector” display. Thats when they are seen before midnight. These last an hour or so before the sun dips down and they lose the illumination for a while. That’s whats been missing over the past few years.
Where are you (approximately)? If you’ve never seen them then persevere, it’ll be worth it. They can be more beautiful than any tropospheric cloud if you hit it lucky.I remember one night in 2006 when there was a cracker. I have never seen anything like it before or since. Strange long tendrils curling over the sky, really weird. Sadly no pictures as I had packed up at the observing site and at 3.30am was just too tired to un-pack the kit.
cheers,
Bill. -
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http://earthobservatory.nasa.gov/IOTD/view.php?id=48892
I stumbled across this when trying to follow Graham in another topic – for some reason I have a thumbnail/icon (?) permanently on my background of ‘Arctic Oscillation’ and this is the next image, it says.
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Hi,
Yep, I remember seeing that a while back.
But as far as I can tell they are looking at slightly different things.Polar Mesospheric Clouds exist over, well, the polar regions. The satellite instruments are looking at purely UV data. This limits the size of particle that are observed.
So what they are seeing isn’t the same as the visual NLC that we as humans observe.
They are probably related (I once read the line somewhere that NLC’s were the ragged southern edge of the PMC sheet) but the AIM satellite does not see NLC it sees PMC.Looking at the graph it only goes back to the 80’s. That’s only a couple of solar cycles and look at the difference in the solar activity over that period. Solar activity has an effect on the amount of UV arriving at the Earth. That in turn has an effect of the photochemisty going on.
The other thing to note VERY carefully is the y axis. These are units with an exponent of 10 e -6. So, far left top line, starts at ~11 e-6 and ends far right at ~ 13 e-6. Since the exponent hasn’t changed this is an increase of 2 parts per million in albedo. (I’m not a geophyisicist but I do have reservations about using the word “large” in their subtext a 2ppm!) It’s even smaller at the lower latitude end….
I don’t know if you’ve open up the papers listed but if I remember correctly there are some graphs where the error bars are bigger than the span of measurements. They also have merged different data sets and I’d bet the radiometery isn’t better than 1% ( that equivalent to 1000 parts per million).It’s presenting stuff such as this using words like “large” to the public that breeds the mild climate hysteria. I could be cynical and say that’s the goal, it improves the grant application chances…
However, these guys are professional scientists, so maybe they’re right but I still urge caution before embuing NLC with overtones of man made doom just yet. Of course, it also why they’re worth watching! ;-)
cheers,
Bill. -
Just to make sure no one misses this NLC, random on the CAS Home page, from the island of some of my ancestors.
https://cloudappreciationsociety.org/gallery/photo-n-3166/
It must be the time of year to keep your eyes peeled (and report back here)
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Hi,
It is indeed the time….
Had a couple of displays so far. Last Saturday was mostly hidden by tropospheric cloud but could be seen in the breaks.
There was another display this morning (2015/6/11-12). Moderate brightness but quite extensive and some nicely detailed features.Picture was taken at 02.27am BST.
Here’s hoping we get better displays as the summer goes on.
Also, if you have a pair of binoculars to hand, have a look at the NLC with them. The detail that can be seen is extraordinary at times. It’s also a good way to help identify faint NLC from twilight illuminated cirrus. The cirrus will not show any of this detail but even faint NLC generally does.
Cheers,
Bill. -
And aurora borealis too?
I suppose the two are not incompatible? The aurora was seen on the UK south coast:
It is not as rare as fog in Phoenix, the link suggests.
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There is a lot of useful info in last year’s NLC thread, so I chose to reply to it today.
You will have noticed the Cloud of the Month NLC picture (Nederlands 2JUN16 ?) and explanations on the CAS Home Page. On 3JUN16 there were NLC in NE UK; the Guardian reports Whitley Bay
http://www.theguardian.com/news/gallery/2016/jun/03/best-photographs-of-the-day-noctilucent-clouds-whitley-bay-assad-airstrikes#img-9whilst The Times (UK) (4JUN16) has a small picture ‘a rare sighting of “night clouds” (sic), which form at the highest reaches of the atmosphere, in Co Durham’.
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